I have a work around for anyone trying to get rid of an old image/thumbnail that just won't go away like the Terminator. Assuming you have already deleted the image & any links to that image. Just copy and paste up a new note with all the old info in it as it stands now updated. And have another other large sized image placed preferably at the top of the note that you prefer to see. Again so copy the old note and then paste it into a new replacement note. Then after carefully checking which is the old note I delete it. The new note will show the new photo you prefer to see. Of course there should be an easier way to do this but this work around does the trick for me!!!